The present invention relates to a drop-on-demand (hereinafter, abbreviated DOD) type ink jet head.
Among non-impact printers, which have a widely expanding commercial market, the ink jet printer is the one which has the simplest principle of operation and is suitable for color printing. Among such printers, the so-called DOD type ink jet printer, which ejects ink droplets in a dot-formation is currently the most commercially important. Examples of DOD type ink jet printers include a Kaiser type, which is disclosed in Japanese Publication No. 12138/1978, and a thermal jet type, which is disclosed in Japanese Patent Publication No. 59914/1986. However, the Kaiser type printer has the disadvantage that it cannot be easily miniaturized, and the thermal jet type printer has the disadvantage that the ink tends to burn due to the application of intense heat.
So as to simultaneously overcome the above-described disadvantages, Japanese Laid-Open Patent Publication No. 159358/1984 proposes an expansion mode type ink jet head which uses deformation in an expansion mode of strips made of piezoelectric material. Japanese Laid-Open Patent Publication No. 252750/1988 proposes a shear mode type ink jet head which uses deformation in a shear mode of strips made of piezoelectric material.
FIG. 35 is a cross-sectional view illustrating the structure of the ink jet head disclosed in Japanese Laid-Open Patent Publication No. 159358/1984. The strips 352b, 352c, 352d made of piezoelectric material such as PZT (lead zirconate titanate) are fixed in parallel on the supporting plate 1 of the electrically conductive material. The upper parts of the strips are fixed to an insulating lid 3. On a surface of the lid 3 to which the strips are fixed, electrodes 354bc, 354de are formed in advance. The channels formed between each of the strips include, in alternating succession ink filled ink-flowing passage 355bc, 355de and dummy channels 356ab, 356cd, 356ef which are filled with an elastic material. One end of each ink channel is connected to a common ink reservoir for supplying ink. The other end of each ink channel is covered by a nozzle plate having small holes 10.
The strips made of piezoelectric material are polarized in one direction as shown by arrow 7 (or in the direction opposite thereto). When a negative electric potential is applied to the electrode 354bc relative to the electrically conductive supporting plate 1, the strips 352b, 352c made of piezoelectric material reduce in thickness and the deformation in the expansion mode produces an increase in width. As a result, the cubic volume of the ink channel 355bc is reduced, and the pressure of the ink in the ink channel 355bc is instantaneously increased so as to cause an ink droplet to be ejected from the nozzle hole 10.
FIG. 36 is a cross-sectional view illustrating the structure of the shear mode type ink jet head of Japanese Laid-Open Patent Publication No. 252750/1988. Barriers 362a, 362b, 362c are formed by forming grooves in a plate made of piezoelectric material. The upper ends of these barriers are adhered to a lid 3 by an elastic material 360. The resulting channels include alternating ink channels 365bc, 365de and dummy channels 366ab, 366cd similar to the expansion mode type ink jet head. A common ink reservoir and holes 10 are also provided.
The piezoelectric plate 1 and the barriers are polarized as illustrated by arrows 7. Electrodes 364ab, 364bc, 364cd are formed on the inner wall of each channel.
When a negative electric potential is applied to the electrodes 364bc, 364ab, as illustrated in FIG. 36, the barrier 362b is deformed in the shear mode by interaction between an electrical field shown by the lines 16 of electric force produced by the electric potential and the polarization 7. If negative electric potential is applied to the electrodes of the barriers, the volume of the ink channel 365bc is reduced instantaneously from an initial state (such as that shown for the ink channel 365de) and the ink droplet is ejected from the nozzle hole 10.